The present invention relates to fluid dynamic energy storage and producing devices and, in particular, to such devices having a loop arrangement wherein a low density substance is injected into a fluid within one leg of the loop so as to create a dynamic circulation of the fluid therein which circulation of the fluid is passed through an electrical generating device so as to produce energy.
Electrical generation companies normally operate on a power grid system, wherein numerous individual power plants of the fossil fuel type, nuclear type, or the like are joined together over common transmitting lines. These grid systems typically experience substantial swings in power usage, depending on seasons, weather, and time of day. Such power grids usually have certain base power production plants which operate during low power demands. One or more of such base plants may be varied in power output to accommodate savings in power output required by the grid. Such variation in power output tends to be harmful to the plants. In addition, during peak demands, additional relatively low efficiency plants are placed on the line. Because of the need to satisfy peak load demand, sufficient power plants must be available to the grid system to meet such peak loads at a relatively high cost for building and operating each plant. On the other hand, relatively few plants are necessary for average power usage periods. Thus, substantial capital outlays may be expended for power plants which are utilized only during peak power consumption periods, thereby increasing the overall average cost of electricity to a use in the grid system. It is also noted that start-up and shut-down of power plants is typically harmful to equipment and reduces the operating hour-life expectancy of such equipment.
It has therefore been suggested that a method be developed wherein the number of power plants, which are required to produce the average amount of electricity used by the grid system, would be operated on a somewhat continuous basis without adding additional power plants for peak periods. This would be accomplished by somehow storing the electrical energy generated by the power plants during low usage periods and utilizing the stored energy during high usage periods. Various methods have been proposed for accomplishing such an energy storage and retrieval concept. For example, two reservoirs may be located at vertically spaced positions. A conduit is utilized to connect the two reservoirs and contains a hydroelectric generator. During peak periods, water is allowed to flow from the upper reservoir to the lower reservoir, past the generator, so as to produce electricity. During low usage periods, electricity from the grid system is utilized to operate pumps which transfer the water from the lower reservoir back to the upper reservoir. A problem inherent with the prior art systsm has been generally that they are relatively inefficient, such that substantially more energy must be input to the system than can be withdrawn therefrom.
The present invention is partially based upon the concept that injection of a low density substance into a higher density fluid in one leg of a loop so as to substantially modify the density of the fluid in that leg will create a circulation within the loop. If a hydroelectric type generator is placed within the loop, the energy of the circulating fluid can be withdrawn. The concept of injecting a gas into a liquid in the manner so far described has been shown in the prior art. However, the prior art has injected gas into the liquid to effect a transporting phenomena which requires a substantial amount of work and does not produce a very highly efficient system. In particular, the prior art devices have typically required heating or some other means to actually lift the fluid or to change the density of the fluid on one side of the loop. This is occasioned by the design of the prior art devices which have not provided expansion in the riser leg of the loop, wherein the gas is injected, so that the fluid is free to expand generally in proportion to the reduction in density thereof. Although applicant does not wish to be tied to a particular theory, it is believed that the expansion of the riser at the point of injection of the gas, such as is provided herein, maximizes the effects of gravity and buoyancy while requiring a minimum amount of work to inject the gas into the fluid. Applicant has also found that utilization of foaming or surface tension enhancing agents in conjunction with gaseous channeling reducing devices within the riser tends to increase the overall efficiency of the device.
The amount of work required to inject a gas into a fluid, as in the present invention, is generally proportional to the pressure sensed in the fluid at the point of injection of the gas which in turn is proportional to the density of the fluid above the point of injection and the velocity of the fluid flowing past the injection point. Thus, as the density of the fluid decreases, the pressure required to inject the gas also decreases and, therefore, the work per unit volume of gas injected also decreases. On the other hand, additional quantities of gas must be injected into the system to effect reduced densities in the fluid; this in turn requires additional work to compress the gas, although it is being compressed at a lower pressure. Calculations show, when all of the work input is calculated, that at relatively low densities (at or below 30 percent of the normal fluid density), the amount of work required to compress and inject the gas into the fluid becomes approximately equal to or less than the amount of work produced by the generator. The efficiency of the system is apparently substantially enhanced by the relatively increasing effects of the forces related to gravity and buoyancy as the density of the fluid decreases within the riser.